Conventionally, the ignition devices that use the plasma generator that generates the electromagnetic wave plasma by irradiating the electromagnetic wave into the combustion chamber of the internal combustion engine, has been suggested as the ignition devices for ignition procedure in the internal combustion engines. For example, in Japanese unexamined patent application publication No. 2009-38025, and Japanese unexamined patent application publication No. 2006-132518, the ignition devices of the internal combustion engine that use such kind of plasma generator are disclosed.
In Japanese unexamined patent application publication No. 2009-38025, the plasma generator in that the spark discharge is generated at the discharge gap of the spark plug, the microwave is irradiated toward the discharge gap, and the plasma is expanded, is disclosed. In such plasma generator, the plasma generated by the spark discharge receives energy from the microwave in pulse. Thereby, electrons at the plasma region are accelerated in speed, ionization is induced, and plasma volume increases.
In Japanese unexamined patent application publication No. 2006-132518, the ignition device of the internal combustion engine in that the plasma discharge is caused by irradiating the electromagnetic wave into the combustion chamber from the electromagnetic wave irradiator, is disclosed. On the top surface of the piston, the electrode for ignition that is insulated from the piston is provided. The electrode for ignition plays a role, in the vicinity thereof, of increasing locally the electric field strength of the electromagnetic wave inside the combustion chamber. Thereby, in the vicinity of the electrode for ignition, the plasma discharge is caused.